This invention relates to fastener assemblies of the type which employ an expandable screw body defining a cavity therethrough into which an elongated spindle having a cone shaped end portion is forced to expand an end portion of the cavity and screw body to lock the latter with the surrounding threads of a nut, tapped machinery mounting bracket, engine block bore or the like. This invention also relates to means for locking such a spindle at a desired position within the screw body to prevent accidental slippage of the spindle which might cause the screw body to unlock from an interiorly threaded member to which it is fastened.
Broadly speaking, such expandable fastener assemblies have long been known in the prior art. See, for example, U.S. Pat. No. 990,065 issued to A. L. Sargeant on Apr. 18, 1911; British Pat. No. 161,871 published Apr. 21, 1921; German Pat. No. 362413 published Jan. 27, 1923; and U.S. Pat. No. 3,042,094 issued to M. J. Liljeberg on Jul. 3, 1962. These reference patents all show expandable bolts or screw bodies which have slots formed in a threaded end portion thereof and define a cavity extending therethrough into which either a threaded expansion rod or smooth draw rod or spindle having a cone shaped end portion is inserted. In the German patent, the cavity is uniformly cylindrically shaped from one end to the other while, in each of the remaining patents, an end portion of the fastener cavity is frusto-conically shaped and tapered in conformity with the shape and taper of a cone shaped end portion or boss on a rod or spindle.
A problem which occurs in cases where the cone shaped boss on the spindle is of essentially the same size, shape and taper as the cone shaped end portion of the bolt cavity into which it is forced, is that an interior portion of the cavity is first to engage the boss. Thus, an interior annular portion of the cone shaped cavity portion begins to expand radially outwardly such that an annular gap or space occurs between an end of the cone shaped cavity at it's opening on the end of the threaded bolt body and an annular surface portion of the boss which lies in the plane containing the end of the bolt body. Such an annular gap or spacing permits a threaded end portion of the bolt body to wobble on the spindle which sets up stresses in the bolt body in a central region thereof surrounding an interior end portion of the boss which is tightly jammed against an interior end portion of the cone shaped cavity. Such stresses have been known to cause the expandable bolt body to fracture in this central region and thus fail. If the bolt is one used to secure an aircraft engine to an air frame, for example, it is obvious that such a failure can produce disastrous consequences.
Another problem that has been encountered using prior art expandable bolts to secure massive components together relates to the means used to lock the expansion rod or spindle at a desired position within the bolt cavity such that the spindle will not accidentally slip longitudinally to produce contraction of the surrounding bolt threads to thus decouple the bolt from the interiorly threaded member to which it is joined. Such slippage can occur in the reference devices due to vibration which is sufficient to loosen the spindle retaining nut which is engaged with a threaded end portion of the spindle on one end of the bolt body. To prevent such loosening, a cotter key has been used in the prior art which is inserted through a passage which extends through the side of the spindle retaining nut and through as aligned passage through the threaded end portion of the spindle. However, it is sometimes difficult to obtain the precisely desired position of the spindle in bolt cavity and securely tighten the spindle retaining nut against an end of bolt body and, at the same time, secure alignment of the passageways through the nut and spindle for insertion of the cotter key therethrough. Moreover, it is sometimes difficult to remove such a cotter key from the passageways when it is desired to remove the expandable bolt from the threaded member with which it is joined because of a slight misalignment in the nut and spindle passages which can occur due to vibration over a period of time after the assembly has been installed.
By means of our invention, these and other problems encountered using prior art expandable bolts and conventional locking means therefor are substantially reduced, if not altogether eliminated.